New tech allows moon events to be accurately synchronised from Earth, paving the way for more spacecraft and people to work on the satellite. — SCMP
Chinese researchers have released the world’s first software for lunar timekeeping, a tool designed to support precise navigation and landings as a new global race to the moon gathers pace.
Clocks tick faster on the moon than on Earth due to weaker gravity – by about 56 millionths of a second per day. The effect, predicted by Albert Einstein’s theory of general relativity, is tiny but accumulates over time, making Earth time increasingly unreliable for lunar operations.
To address this, a team from the Purple Mountain Observatory in Nanjing built a model that accounts for both the moon’s weaker gravity and its motion through space, allowing events on the moon to be accurately synchronised with clocks used on Earth.
The researchers reported that their method remained accurate to within a few tens of nanoseconds even over 1,000 years, according to a paper published in the December issue of Astronomy and Astrophysics.
They also packaged the model into ready-to-use software, enabling users to compare lunar and Earth time in a single step instead of relying on complex calculations. The team said the goal was to make lunar timekeeping practical as missions to the moon become more frequent.
Jonathan McDowell, a Harvard astronomer and space historian, said lunar timekeeping was becoming a real engineering need rather than something that could be handled on a case-by-case basis using Earth time, as in the past.
Differences as small as a microsecond could quickly become significant in navigation systems, affecting calculations over timescales of a minute, he said.
“If you want to use the equivalent of GPS on the moon – which we’ll probably want to do in just a few years from now, especially for precision landing locations – you’ll need to handle this somehow.”
McDowell said while similar work had been under way in the US, he was not aware of another readily available tool. “This emphasises that China is serious about the moon, and is being quite open about sharing its lunar-related research,” he said.
In the past, the fact that clocks tick differently on the moon and on Earth mattered little because lunar missions were rare. Engineers simply used Earth time and applied corrections for each mission when needed.
That approach is becoming harder to sustain. As more spacecraft – and eventually people – are expected to operate on and around the moon at the same time, relying on ad hoc fixes would quickly become unwieldy.
To prepare for that future, the International Astronomical Union adopted a broad framework in 2024 calling for the moon to have its own time reference.
Building on that framework, the Chinese team set out to turn the idea into something engineers could actually use. They began by using precise data on the moon’s motion to track how the time difference between the moon and Earth changes over time.
They then wrapped those calculations into a software package that automates the process, allowing users to compare lunar and Earth time directly instead of performing complex calculations themselves.
The team named the software LTE440, short for Lunar Time Ephemeris. They noted that it was an early step and would need to be extended to support real-time navigation and future lunar clock networks. – South China Morning Post
